This invention relates to an apparatus for mixing a resin and a catalyst and, more particularly, to an apparatus for efficiently mixing a high viscosity heavily filled resin with a catalyst, quickly and without requiring hazardous solvent to clean the apparatus after use.
Resins have numerous uses including, but not limited to the construction of swimming pools, the exterior coating of buildings, the protective interior coating of tanks, as well as the protective coating of secondary containment walls. A resin such as polyester is typically applied to a surface with a catalyst such as methyl-ethyl-ketone peroxide. Catalysts allow the resin to polymerize and cure. The present state of the art methods of resin application involve the spraying of the resin and methyl-ethyl-ketone peroxide onto a particular surface with either an internal mix or external mix spray gun.
An internal mix gun is often used when solvent emissions are a problem, because internal mixing limits the amount of atomized material and catalyst exiting the gun. Internal mix guns generally have at least two feed lines, a resin line and a catalyst line, which feed into a manifold. The resin and catalyst are typically mixed in this manifold. After mixing, the resin and catalyst are expelled from the gun in confluence and under pressure through a nozzle or similar orifice. The resin and catalyst are expelled from the gun with sufficient pressure to atomize the resin and catalyst mixture and give the article being sprayed an even coat of catalyzed resin. A major drawback of this type of gun is that when a spraying operation is completed, the catalyzed resin remaining within the manifold begins to harden. If not removed from the manifold, the hardening resin will often set up within the manifold. Resin which has hardened within the manifold is extremely difficult, if not impossible to remove. Removal of hardened resin requires expensive and time-consuming cleanings. Often removing hardened resin from a manifold causes so much damage to the manifold that the costly manifold must be discarded.
To remove resin from the manifold after a spraying operation, most internal mix guns are equipped with a third feed line. This feed line supplies acetone or similar solvent to the manifold to flush the manifold after completion of a spraying job. While such a flushing system is typically adequate to dislodge most of the resin from the manifold, the solvent cannot remove all of the catalyzed resin. O-rings within the gun, used to surround check valves, often become so irreparably damaged by resin build-up that the gun must often be rebuilt or discarded.
A larger problem with the internal mix gun is the use of a solvent and the disposal thereof. Acetone and methylene chloride are the most popular solvents for internal mix guns, but have recently come under strict regulation due to their harmful effects on humans and the environment. Waste solvent from manifold cleaning poses a threat to humans and the environment. In an operation with many guns, which must be flushed hundreds of times per day, the accumulated waste solvent becomes a serious environmental hazard. Government regulations are moving toward a complete ban of all outdoor solvent flush. Although it is possible to reclaim waste solvent through the use of a reclaimer, these devices are extremely costly in terms of both time and money. Furthermore, even a reclaimer produces hazardous "still bottoms" which add to landfill contamination.
The second type of gun typically used is an external mix gun. In an external mix gun, the resin and catalyst are atomized and expelled separately and directed toward one another. The resin and catalyst combine in the air shortly before contacting the article being treated. With the external mix gun, the manifold and solvent flushing are eliminated along with the accompanying disposal problems. A major drawback of the external mix gun, however, is the incomplete mixing of resin and catalyst, which often leads to patches of incompletely catalyzed resin appearing on the finished article. Such portions of uncatalyzed resin can produce points of weakness or blisters on the surface of the finished article.
A more important problem with external mix guns is the exterior atomization of the catalyst. Because of the incomplete mixing of the catalyst with the resin, much of the atomized catalyst disperses into the atmosphere and, more particularly, in the immediate work environment where the application is taking place. Concern over the safety of workers breathing catalyst contaminated air has led to numerous restrictions on the use of external mix guns. Such guns have even been completely banned in at least one state.
The difficulties encountered in the prior art discussed herein above are substantially eliminated by the present invention.